John, I wonder two things: When you are using different volumes of developer (250, 500 and 1000ml), are you using the appropriate volume of PMK stock, or are you using a set amount and using more or less water, thereby varying the dilution ratio? Two, when you are developing one roll in 250, 500 and 1000ml, are you filling an appropriate sized tank, or are you developing, for example, one roll in 250ml of developer in a 1000ml tank?(posted 8398 days ago)Assuming you are using a consistent dilution ratio and you are completely filling your developing tank, the only other things I can think to check are your water pH, and as previously posted, your redevelopment procedure and wash duration. If you are not using distilled water for developing, I recommend you try a roll with distilled water. It's possible that your water is slightly acidic, thereby neutralizing the alkalinity of your developer, which will limit staining.